Why people seem willing to be my friends at first but eventually they avoid me?

I started to hang out with two guys my age at school and two girls. One girl stopped hanging out with us and later on my three new friends started to ignore me I was like their tail. I had a small talk with a girl who seem so excited to talk to me the first time, but a week later we had an hour conversation and after that she didn't seem interested.

It's been awhile since I don't make new friends. So I have forgotten what to expect from people, or how are they likely to act once they have gotten to know you better.